We also know of the Great Oxidation Event [1], and that life on earth is older than that. Animals are recent-ish (~500mya) but single cell organisms that do no

We also know of the Great Oxidation Event [1], and that life on earth is older than that. Animals are recent-ish (~500mya) but single cell organisms that do not require oxygen must exist. [1] https://en.wikipedia.org/wiki/Great_Oxidation_Event https://en.wikipedia.org/wiki/Great_Oxidation_Event